This disclosure relates to containers, and more particularly to containers that experience negative internal pressure after being filled, sealed, and capped.
It has been a goal of conventional container design to form container bodies that have a desired and predictable shape after filling and at the point of sale. For example, it is often desired to produce containers that maintain an approximately cylindrical body or a circular transverse cross section. However, in some instances, the containers are susceptible to negative internal pressure (that is, relative to ambient pressure), which causes the containers to deform and lose rigidity and stability, and results in an overall unaesthetic appearance. Several factors can contribute to the buildup of negative pressure inside the container.
For instance, in a conventional hot-fill process, the liquid or flowable product is charged into a container at elevated temperatures, such as 180 to 190 degrees F., under approximately atmospheric pressure. Because a cap hermetically seals the product within the container while the product is at the hot-filling temperature, hot-fill plastic containers are subject to negative internal pressure upon cooling and contraction of the products and any entrapped air in the head-space. The phrase hot filling as used in the description encompasses filling a container with a product at an elevated temperature, capping or sealing the container, and allowing the package to cool.
As another example, plastic containers are also often made from materials such as polyethylene terephthalate (PET) that can be susceptible to the egress of moisture over time. Biopolymers or biodegradable polymers, such as polyhydroxyalkanoate (PHA) also exacerbate egress issues. Accordingly, moisture can permeate through container walls over the shelf life of the container, which can cause negative pressure to accumulate inside the container. Thus, both hot-fill and cold-fill containers are susceptible to the accumulation of negative pressure capable of deforming conventional cylindrical container bodies.
Conventional containers include designated flexing portions, or vacuum panels, that deform when subjected to typical negative internal pressures resulting from the hot filling process. The inward deflection of the vacuum panels tends to equalize the pressure differential between the interior and exterior of the container to enhance the ability of the cylindrical sections to maintain an attractive shape, to enhance the ease of labeling, or to provide like benefit.
Some container designs are symmetric about a longitudinal centerline and designed with stiffeners to maintain the intended cylindrical shape while the vacuum panels deflect. For example, U.S. Pat. Nos. 5,178,289; 5,092,475; and 5,054,632 teach stiffening portions or ribs to increase hoop stiffness and eliminate bulges while integral vacuum panels collapse inwardly. U.S. Pat. No. 4,863,046 is designed to provide volumetric shrinkage of less than one percent in hot-fill applications.
Other containers include a pair of vacuum panels, each of which has an indentation or grip portion enabling the container to be gripped between a user's thumb and fingers. For example, U.S. Pat. No. 5,141,120 teaches a bottle having a hinge continuously surrounding a vacuum panel, which includes indentations for gripping. The hinge enables the entire vacuum panel to collapse inwardly in response to negative internal pressure.
What is desirable is a container capable of deflecting at an inconspicuous location in response to the accumulation of negative internal pressure.